Three years in, AMOLED displays are finally getting it right

The Galaxy S 4's display is a sizable step forward for PenTile AMOLED, according to DisplayMate's Raymond Soneira.

Florence Ion

We've already given you our subjective impressions of Samsung's Galaxy S 4 and its 1080p AMOLED display, but for those of you who hunger for quantitative data, Dr. Raymond Soneira of DisplayMate has given the phone an in-depth shakedown. Soneira compares the screen's brightness, contrast, color gamut, and power consumption to both the Galaxy S III (which also uses an AMOLED display) and the IPS panel in the iPhone 5. What he found was that Samsung's AMOLED technology is still fighting against some of its inherent weaknesses, but it has made great strides forward even since the Galaxy S III was released last year.

To recap: both the S III and S 4 use PenTile AMOLED screens, which use a slightly different pixel arrangement than traditional LCD screens. A pixel in a standard LCD panel has one red, one green, and one blue stripe; PenTile uses alternating red-green-blue-green subpixels, taking advantage of the eye's sensitivity to green to display the same image using fewer total subpixels. These screens cost less to manufacture but can have issues with color accuracy and text crispness. The backlight for each type of display is also different—white LEDs behind the iPhone's display shine through the red, green, and blue subpixels to create an image, while the AMOLED subpixels are self-lit. This has implications for brightness, contrast, and power consumption.

A close-up shot of PenTile AMOLED in the Nexus One, when the tech was much less mature.

Luke Hutchinson

We'll try to boil Soneira's findings down to their essence. One of the S 4's benefits over its predecessor is (obviously) its pixel density, which at 441 ppi is considerably higher than either its predecessor or the iPhone 5. Soneira says that this helps it to overcome the imbalance between PenTile's green subpixels and its less numerous red and blue ones, which all but banishes PenTile's "fuzzy text" issues:

…for digitally generated fine text and graphics with precise pixel layouts the eye can visually detect the reduced number of Red and Blue sub-pixels unless the number of Red and Blue Sub-Pixels Per Inch is very high. And it is for the Galaxy S4—there are 312 Red and Blue Sub-Pixels Per Inch, which is only a few percent lower than Apple’s Benchmark 326 PPI iPhone Retina Display.

As for color accuracy, some of the S 4's five different display modes are better than others. The default Standard Mode presents more saturated colors, which may draw the eyes of people looking for their next smartphone in their carrier's store, but these colors aren't actually very accurate. Soniera recommends using the phone's Movie Mode for the most accurate colors (though it's still slightly too green) in most cases. Photographers should also note that the phone's Photo Mode "provides a fairly accurate calibration to the Adobe RGB standard, which is rarely available in consumer displays."

The iPhone 5 (right) still has an excellent display, but the S 4 is catching up.

Jacqui Cheng

The Galaxy S 4's AMOLED display still lags behind the iPhone 5's LCD display in brightness, but it outdoes its predecessor. The S III's maximum brightness is only 283 cd/m2 while the S4's does much better at 475 cd/m2. The iPhone 5's display still gets a bit brighter at 556 cd/m2, but Samsung has made definite strides here.

Viewing angles are a bit of a toss-up: the Galaxy displays are both brighter at extreme viewing angles, but the iPhone's colors shift less. Also note AMOLED's typically excellent contrast ratio.

Finally, Soneira looks into the power consumption of all three screens, where the iPhone 5 once again edges out both Samsung handsets, but the S 4 makes considerable forward strides. Using the same screen brightness settings and the same amount of screen area for each phone, he found that the S 4's screen consumed 0.70 watts of power, compared to 0.83 watts for the S III and 0.66 watts for the iPhone 5. It's worth noting, though, that the S4's increased maximum brightness can cause its screen to consume more power than the S III's screen at its maximum brightness: 1.5 watts compared to 1.3 watts (compared to a much lower 0.74 watts for the iPhone 5).

Overall, Soneira's extensive testing shows that PenTile AMOLED screens are slowly overcoming their limitations while holding on to their traditional strengths (cost and contrast ratio, primarily). The S III's screen is by no means bad, but the S 4 improves on it in just about every way, and both screens are worlds ahead of where the technology started out in 2010 when the Nexus One launched.

"The Galaxy S4 continues the rapid and impressive improvement in OLED displays and technology," writes Soneira. "The first notable OLED Smartphone, the Google Nexus One, came in decidedly last place in our 2010 Smartphone Display Shoot-Out. In a span of just three years OLED display technology is now challenging the performance of the best LCDs."

Would appreciate a more detailed explanation of the benefits of AMOLED. The article talks mostly about how its catching up but the obvious question is why would anyone bother if its just catching up.

I haven't had too much experience with AMOLED's on hand.

AMOLED screens show black as no light and the power used by the screen is dependent on the colors shown on it. So if most of it is black with some grey text it uses little power. Darker colors use less power.

Would appreciate a more detailed explanation of the benefits of AMOLED. The article talks mostly about how its catching up but the obvious question is why would anyone bother if its just catching up.

I haven't had too much experience with AMOLED's on hand.

As the article says, cost and contrast. This results in the amazing blacks you see (you don't have the problem of trying to 'block' the backlight like with LCD) and that they're cheaper to produce is an obvious benefit in keeping costs down.

The big benefit is being able to kill power to produce black. If the lit part can reduce power too there's really big gains to be had.

As the article says, cost and contrast. This results in the amazing blacks you see (you don't have the problem of trying to 'block' the backlight like with LCD) and that they're cheaper to produce is an obvious benefit in keeping costs down.

And this says something about the relative efficiency of the iPhone backlight LEDs and the OLED technology used in the display. The former uses filters to block 2/3 of the light it uses from going through each subpixel...and the latter still uses more power and gets lower brightness?

OLED displays have the potential for significant efficiency gains because they don't produce light only to filter most of it out. I didn't expect them to have an overwhelming advantage over conventional LED backlights this soon, but I'm a bit surprised they're still catching up...

An "Infinite contrast ratio" for the AMOLED screens? Really? I always thought that was just marketing BS.

I'd say because the AMOLED simply turns the pixels off to show black, thus zero light escapes from a black screen, whereas LED displays keep on shining the backlight at pixels that are (mostly?) opaque to show black. So for amoled the contrast ratio results in a div by zero --> infinity.

Now theoretically he bright white can still be a weak washed out mess and still achieve "infinite" contrast by virtue of zero black light, so I can't see how the ratio is is useful information when one could compare to a hypothetical display with a very low black, very bright whites and a large (but non-infinite!) contrast ratio.

I'm interested in the power usage tests - I assume "the same amount of area" is normalising power use for screen size, but what was the displayed image, were various colours and coverages used?

LED displays would be relatively constant across all image types (unless iphones have variable backlighting like some fancy TVs?), whereas AMOLED power usage is highly sensitive to the colours being shown - a mostly black image will spend zero energy lighting up the dark portions, etc.

(In theory the Ars white-on-black theme lets one read longer on such a display )

An "Infinite contrast ratio" for the AMOLED screens? Really? I always thought that was just marketing BS.

Pixels in OLED screens emit light rather than act as filters for a backlight like LCD pixels. The ratio for OLED screens is infinite because black OLED pixels emit no light, whereas LCD pixels aren't perfect and never block 100% of the backlighting.

An "Infinite contrast ratio" for the AMOLED screens? Really? I always thought that was just marketing BS.

This is because AMOLED completely turns off to "generate" black.LCD's just tries to block the backlight from shining through.

The contrast ratio is measured between the brightest white and the darkest black.In the case of the AMOLED, the darkest black would always be measured at zero, resulting in an infinite contrast ratio. Even if the screen isn't super bright.

Felt a bit like groundhog day reading through the comments, but at least they're pretty consistently giving good info

Interesting to note on the contrast ratio side how it does sort of become a useless measure with OLEDs.

On the power consumption side, I think a more interesting measure would be the power consumption per square inch if you want a purely oranges to oranges comparison (would be weird using 'apples' in the phrase). i.e. what would the power consumption be for a pentile screen at the same physical dimensions as an iphone 5. (Of course that begs the question of whether that value changes dramatically with a higher pixel density...so complex!).

Interesting stuff though, I guess the good news is that pentile might finally start looking like it won't inherently make people cringe when they read it on a spec sheet because we're at the point it just doesn't really matter that much with such high PPI values.

Would appreciate a more detailed explanation of the benefits of AMOLED. The article talks mostly about how its catching up but the obvious question is why would anyone bother if its just catching up.

I haven't had too much experience with AMOLED's on hand.

The biggest advantage has always been contrast ratio. All LCD's average about 1000:1, which is OK for use in bright environments and / or bright content.

The problem with LCD's is it's low light performance, like say during a night scene in a movie. (like for example Harry Potter movies, which have lots of night scenes)LCD falls apart with such content, and it shows it's limitations in a very unpleasant way:Things that should look dark actually look gray instead. This kills picture quality for content like that. (even more noticeable with the lights off, since your eyes adjust to let more light in)

Now, I've never really been bothered by that limitation on a phone, since i mostly use it in bright environments and rarely use it to view movies. So I've always preferred the higher PPI and proper grayscale and gamut calibration of the iPhone 4 and above to the superior, but un-calibrated color pallet of OLED.(see, for some reason we still use sRGB as the color standard, even though AMOLED can handle a much wider color gamut, but since the AOMED screens come un-calibrated the result is over-saturated colors when displaying sRGB content)

So, now that AMOLED is letting us have our cake and eat it, I see no reason why i would want an LCD over AMOLED at all. They finally got an sRGB profile and the fact that they are using pentile is now a moot point. I can't wait to see one for myself, and i'd love one of these on an oculus rift.

The advantage of AMOLED becomes extremely obvious at night, where one can reduce power consumption of a display by at least 66% when switching to the monochromatic mode.

I have a shortcut on my device which switches the screen to black background (no power) and red foreground (only 33% of power). This also makes it very nice on the eyes at night (this is one of the reasons why special ops. use red light flashlights as the eyes do not have to readjust). Achieving the same effect with the IPS display is pretty much impossible. This feature is especially useful for night time reading as it does not have the same psycho-stimulating effect as the back lit sources.

I do a lot of before sleep reading on my Nexus 10 tablet and no amount of brightness adjustment (even on the lowest setting it is extremely bright for the dark room) or various 'color filter applications' provide a satisfactory night time reading adjustments .

The former uses filters to block 2/3 of the light it uses from going through each subpixel...

You mean 5/6th. A subpixel can only transmit one polarization of each color through a subpixel. So 3 channels times two polarizations mean 1/6 of the light gets through at most. In reality its much less.

Yeah, but mostly because thats a really stupid way to test. Basically two things are at work here:

1) Semiconductor LEDs are incredibly efficient, way more so then organic LEDs2) LCDs are enormously inefficient, particularly for anything but a solid white screen at max brightness.

So what happens is that if you test full white (the absolute worst case for OLED and best for LCD), its roughly a tie. If they'd tested a solid green screen, or white text on a black background, OLED wins by a huge margin. For real world stuff, OLED wins by some amount.

Have Samsung managed to get rid of the blue hue which is the general characteristic of all their displays?

I'm more concerned about display longevity and pixel fade. There was not up one word about it in the article.

Phones aren't used enough for this to be an issue. It only matters for TVs because you run them for hours at a time and keep them for many years. The lithium battery will die many times over before any real aging happens in an AMOLED phone screen pixel.

Interesting. I haven't looked into it, but I've seen comments about the Samsung's colour accuracy being a little off for reds and oranges - too saturated. I'll have to see if I can track down the comments.

The former uses filters to block 2/3 of the light it uses from going through each subpixel...

So what happens is that if you test full white (the absolute worst case for OLED and best for LCD), its roughly a tie. If they'd tested a solid green screen, or white text on a black background, OLED wins by a huge margin. For real world stuff, OLED wins by some amount.

In theory anyway.

In practice, OLED have a small advantage for mixed media (like video) but when it's pure white, can use almost double the power (but is less bright).

I still prefer OLED though. A lot of websites have white on black so I'm covered in that area.

A big advantage of OLED is the lockscreen showing all kinds of interesting information (time, icons for notifications, active profile, battery percentage, connected network, current song, upcoming events) on my Nokia N9. Since only the pixels that are lit are using energy, it's low-power.

Is there an end benefit for the user with the way pentile subpixels are arranged? Loss of color accuracy in favor of vivid, eye-catching (but false) colors and cheaper manufacturing costs benefit Samsung, not the user. If Samsung was able to make a RGB arrangement for previous phones (SGS2, i think), why not continue that trend?

The former uses filters to block 2/3 of the light it uses from going through each subpixel...

So what happens is that if you test full white (the absolute worst case for OLED and best for LCD), its roughly a tie. If they'd tested a solid green screen, or white text on a black background, OLED wins by a huge margin. For real world stuff, OLED wins by some amount.

In theory anyway.

Why only in theory? The tests results in this article confirm that worst case OLED == best case LDC.

Andrew Cunningham / Andrew has a B.A. in Classics from Kenyon College and has over five years of experience in IT. His work has appeared on Charge Shot!!! and AnandTech, and he records a weekly book podcast called Overdue.